U.S. patent application number 13/092063 was filed with the patent office on 2011-08-11 for interbody spinal implant inductively coupled to an external power supply.
Invention is credited to Gary Karlin Michelson.
Application Number | 20110196501 13/092063 |
Document ID | / |
Family ID | 22946608 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110196501 |
Kind Code |
A1 |
Michelson; Gary Karlin |
August 11, 2011 |
INTERBODY SPINAL IMPLANT INDUCTIVELY COUPLED TO AN EXTERNAL POWER
SUPPLY
Abstract
An electrical bone growth promotion apparatus for the delivery
of electrical current to an implant surgically implanted between
adjacent bone masses to promote bone growth to areas adjacent to
the implant is disclosed. The apparatus of the present invention
comprises a self contained implant having a surgically implantable,
renewable power supply and related control circuitry for delivering
electrical current directly to the implant and thus directly to the
area in which the promotion of bone growth is desired. The desired
areas of bone growth promotion may be controlled by conducting
negative charge only to the desired location of bone growth
promotion.
Inventors: |
Michelson; Gary Karlin;
(Venice, CA) |
Family ID: |
22946608 |
Appl. No.: |
13/092063 |
Filed: |
April 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12313896 |
Nov 25, 2008 |
7935116 |
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13092063 |
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|
10631309 |
Jul 31, 2003 |
7455672 |
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|
12313896 |
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|
09404396 |
Sep 23, 1999 |
6605089 |
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10631309 |
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08250177 |
May 27, 1994 |
6120502 |
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09404396 |
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Current U.S.
Class: |
623/17.16 |
Current CPC
Class: |
A61F 2/4611 20130101;
A61F 2002/30433 20130101; A61B 17/7074 20130101; A61F 2/30744
20130101; A61F 2002/30153 20130101; A61F 2002/30507 20130101; A61F
2230/0069 20130101; A61F 2002/30179 20130101; A61F 2002/30143
20130101; A61F 2002/30235 20130101; A61B 17/1757 20130101; A61F
2002/30599 20130101; A61F 2002/30774 20130101; A61F 2002/30604
20130101; A61F 2/4603 20130101; A61F 2002/449 20130101; A61F
2002/30787 20130101; A61F 2002/3092 20130101; A61F 2002/30785
20130101; A61F 2002/30261 20130101; A61F 2002/448 20130101; A61F
2220/0033 20130101; A61F 2220/0041 20130101; A61F 2230/0017
20130101; A61F 2230/0026 20130101; A61F 2250/0009 20130101; A61F
2220/0025 20130101; A61F 2002/30789 20130101; A61F 2002/2821
20130101; A61F 2230/0058 20130101; A61N 1/205 20130101; A61F
2002/30879 20130101; A61F 2002/30398 20130101; A61F 2/44 20130101;
A61F 2002/30904 20130101; A61F 2/442 20130101; A61F 2002/30158
20130101; A61F 2002/3085 20130101; A61F 2002/30845 20130101; A61F
2002/4485 20130101; A61F 2310/00023 20130101; A61N 1/0551 20130101;
A61F 2002/2835 20130101; A61F 2002/30843 20130101; A61F 2210/0004
20130101; A61F 2/446 20130101; A61F 2002/30556 20130101; A61F 2/447
20130101; A61F 2002/30777 20130101; A61F 2002/4629 20130101; A61F
2250/0063 20130101; A61F 2002/30579 20130101; A61F 2002/30062
20130101; A61F 2310/00179 20130101; A61F 2002/30797 20130101; A61F
2002/4627 20130101; A61F 2002/30405 20130101; A61F 2230/0082
20130101; A61F 2002/4681 20130101; A61F 2310/00796 20130101; A61B
2090/036 20160201; A61B 17/8875 20130101; A61B 17/1671 20130101;
A61F 2/30767 20130101; A61F 2002/30841 20130101; A61F 2002/4619
20130101; A61F 2002/3037 20130101; A61F 2002/30593 20130101; A61F
2/4455 20130101; A61F 2230/0019 20130101; A61F 2002/30836
20130101 |
Class at
Publication: |
623/17.16 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. An artificial spinal implant for insertion into an implantation
space created between two adjacent vertebral bone masses,
comprising: a housing including: an upper surface and a lower
surface opposite said upper surface, said upper and lower surfaces
being configured to contact and support the adjacent vertebral bone
masses; a leading end for insertion first into the implantation
space and a trailing end opposite said leading end; opposite sides
from said upper surface to said lower surface, and from said
leading end to said trailing end; a mid-longitudinal axis passing
through said leading and trailing ends; a maximum width from one of
said opposite sides to the other of said opposite sides; a height
from said lower surface to said upper surface; a depth from said
leading end to said trailing end, the maximum width of said housing
being greater than each of the height and depth of said housing,
said leading end being curved from said opposite side to said
opposite side; and a hollow chamber; control circuitry in said
hollow chamber; and a rechargeable power supply for energizing said
control circuitry, said rechargeable power supply being configured
for inductive coupling to an external power supply.
2. The implant of claim 1, wherein said upper and lower surfaces
are configured for bone ingrowth.
3. The implant of claim 1, wherein said upper and lower surfaces
include surface roughenings.
4. The implant of claim 1, further comprising an opening having a
central longitudinal axis perpendicular to the mid-longitudinal
axis of said housing.
5. The implant of claim 4, wherein said opening having the central
longitudinal axis that is perpendicular to the mid-longitudinal
axis of said housing as an inner perimeter different to an inner
perimeter of said closeable opening.
6. The implant of claim 5, wherein the inner perimeter of said
closeable opening is larger than the inner perimeter of said
opening having the central longitudinal axis that is perpendicular
to the mid-longitudinal axis of said housing.
7. The implant of claim 1, wherein said control circuitry is
hermetically sealed within said housing.
8. The implant of claim 1, wherein said rechargeable power supply
is a rechargeable battery.
9. The implant of claim 1, further comprising an external power
supply for inductively recharging said rechargeable power
supply.
10. The implant of claim 9, wherein said external power supply
includes a belt with an electromagnetic transmitter.
11. The implant of claim 9, wherein said external power supply
includes an electromagnetic belt coil.
12. The implant of claim 1, wherein said housing includes a portion
made of titanium.
13. The implant of claim 1, wherein said implant is a spinal fusion
implant.
14. The implant of claim 1, wherein said upper and lower surfaces
include a plurality of openings adapted to allow bone growth from
each of the adjacent vertebral bodies through said hollow
chamber.
15. The implant of claim 1, wherein said trailing end includes a
vertical indented portion along the height of said housing, said
vertical indented portion being centered along approximately
one-half of the maximum width of said housing.
16. The implant of claim 1, wherein said housing includes an
opening to said hollow chamber, said opening being closable.
17. An artificial spinal implant for insertion into an implantation
space created between two adjacent vertebral bone masses,
comprising: a housing including: an upper surface and a lower
surface opposite said upper surface, said upper and lower surfaces
being configured to contact and support the adjacent vertebral bone
masses, said upper and lower surfaces including a plurality of
engagement teeth; a leading end for insertion first into the
implantation space and a trailing end opposite said leading end;
opposite sides from said upper surface to said lower surface, and
from said leading end to said trailing end; a mid-longitudinal axis
passing through said leading and trailing ends; a maximum width
from one of said opposite sides to the other of said opposite
sides; a height from said lower surface to said upper surface, the
maximum width of said housing being greater than the height of said
housing; and a hollow chamber; control circuitry in said hollow
chamber; a rechargeable power supply for energizing said control
circuitry, said rechargeable power supply being configured for
inductive coupling to an external power supply; and an induction
coil, a portion of said housing being made from a metallic
material, said housing including an insulating material insulating
said induction coil from said metallic portion of said housing.
18. The implant of claim 17, wherein said upper and lower surfaces
are configured for bone ingrowth.
19. The implant of claim 17, further comprising an opening having a
central longitudinal axis perpendicular to the mid-longitudinal
axis of said housing.
20. The implant of claim 19, wherein said opening having the
central longitudinal axis that is perpendicular to the
mid-longitudinal axis of said housing as an inner perimeter
different to an inner perimeter of said closeable opening.
21. The implant of claim 20, wherein the inner perimeter of said
closeable opening is larger than the inner perimeter of said
opening having the central longitudinal axis that is perpendicular
to the mid-longitudinal axis of said housing.
22. The implant of claim 19, wherein each of said engagement teeth
has a forward facing facet and a reward facing facet inclined
towards each other to form a peak, the peak of each of said
engagement teeth forming a linear portion parallel to the central
longitudinal axis of said opening having the central longitudinal
axis that is perpendicular to the mid-longitudinal axis of said
housing.
23. The implant of claim 17, wherein said control circuitry is
hermetically sealed within said housing.
24. The implant of claim 17, wherein said rechargeable power supply
is a rechargeable battery.
25. The implant of claim 17, further comprising an external power
supply for inductively recharging said rechargeable power
supply.
26. The implant of claim 25, wherein said external power supply
includes a belt with an electromagnetic transmitter.
27. The implant of claim 25, wherein said external power supply
includes an electromagnetic belt coil.
28. The implant of claim 17, wherein said metallic material is
titanium.
29. The implant of claim 17, wherein said implant is a spinal
fusion implant.
30. The implant of claim 17, wherein said upper and lower surfaces
include a plurality of openings adapted to allow bone growth from
each of the adjacent vertebral bodies through said hollow
chamber.
31. The implant of claim 17, wherein said induction coil is wound
along an exterior surface of said housing.
32. The implant of claim 17, wherein said engagement teeth are
spaced apart from one another.
33. The implant of claim 17, wherein said engagement teeth extend
along the entire width of said housing.
34. The implant of claim 17, wherein said housing includes an
opening to said hollow chamber, said opening being closable.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
12/313,896, filed Nov. 25, 2008, which is a continuation of
application Ser. No. 10/631,309, filed Jul. 31, 2003, now U.S. Pat.
No. 7,455,672, which is a continuation of application Ser. No.
09/404,396, filed Sep. 23, 1999, now U.S. Pat. No. 6,605,089, which
is a continuation of application Ser. No. 08/250,177, filed May 27,
1994, now U.S. Pat. No. 6,120,502, all of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to interbody bone fusion devices, and
more particularly to an apparatus and method for the delivery of
electrical current to a spinal fusion implant and to interbody
fusion material for inducing bone growth and aiding in spinal
arthrodesis.
[0004] 2. Description of the Related Art
[0005] The spine may be fused along any of its various surfaces, or
internally within the interspaces of the vertebrae. Various
interbody fusion devices have been developed to promote interbody
fusions of the spine, such as that of Michelson, U.S. Pat. No.
5,015,247, issued on May 14, 1991, Brantigan U.S. Pat. No.
4,743,256, issued on May 10, 1988, and others. Such devices have
helped to achieve spinal fusion by providing structural support,
presenting bone promoting substances to the fusion site, increasing
the surface area available to participate in the fusion, and by
being both self-stabilizing and stabilizing to a spinal
segment.
[0006] During normal bone repair, the area around the fracture of
the bone exhibits negative charge. The application of electrical
current to negatively charge a site in which spinal fusion is
desired simulates the boners own normal repair process and promotes
osteogenesis. The application of electrical current to negatively
charge a site in which osteogenesis is desired, creates an
electrochemical reaction (4e-+O.sub.2+2H.sub.2O- - ->4OH.sup.-)
which lowers the oxygen tension (decreasing the O.sub.2) to
stimulate osteoblastic activity and promote bone formation.
Further, the formation of the hydroxyl radical
(OH.sup.-) raises the local tissue pH which of itself is favorable
to bone production and further promotes increases in the presence
of alkaline phosphatase, a very potent stimulant of bone formation
in its own right. Still further, there appears to be a direct
effect of electrical current to present a negative charge at the
cellular level so as to upset the resting electrical potential of
the cell membrane with a resultant electrical perturbation within
the cell, the net effect of which is promotional to the cellular
activity of bone formation. Finally, the electromagnetic field
generated by the passage of electrical current appears to be
independent of that current (on the basis of magnetism alone) to be
promotional of bone growth, though the mechanism remains
unknown.
[0007] Conversely, the application of electrical current to
positively charge an area of bone inhibits osteogenesis and thus
inhibits bone formation. Therefore, the application of electrical
current to deliver positive charge to an area of bone may be used
to control the bone fusion process so that it does not occur in
undesired areas such as within the spinal canal.
[0008] The bone fusion process is a race against time, for
eventually, the body will give up its attempt to complete that
process. Well-known within the field of surgery is the use of
electrical current delivered internally, or applied externally
relative to a patient's body to promote bone growth and thus
promote the bone healing or fusion process. However in regard to
the spine, none of the interbody fusion devices of the past
incorporate the use of electric current to stimulate bone growth,
to increase the rate of osteogenesis and the spinal fusion
process.
[0009] To date the use of electric current to promote bone growth
in the spinal fusion process has taken two forms. The first is the
use of an internally implanted electrical pulse generator, with a
cathode wire leading from the pulse generator being wrapped about a
bone plug harvested from the patient's body which is then inserted
into the intervertebral space. These devices however have been
continually plagued with problems that include breakage of the lead
wires from the generator to the fusion site and a second surgery to
remove the generator implanted in the patient's body at a remote
location to the fusion site after the service life of the battery
has expired. The power supplies of these implantable generators
have been ineffective due to their limited service life, which may
be shorter than the time needed to attain solid fusion, and
problematic due to the potential for tissue damage in the event of
a leak. The latter concern prompts most physicians to perform a
second surgical procedure to explant the generator and internal
battery supply. The additional surgery to explant the device
increases the risk of infection and danger to the patient, and
results in unnecessary additional costs.
[0010] The second form in which electric current has been used in
the past to stimulate spinal fusion required the wearing, external
to the body of the patient, of an electromagnetic coil or coils.
Unfortunately, neither of these methods when utilized in
conjunction with the known methods of interbody arthrodesis has
proven fully effective.
[0011] Therefore, a need exists for the means and method of
improving upon and/or perfecting the conjoined use of an improved
interbody fusion device other than bone alone, and the promotion of
bone growth with electrical current.
SUMMARY OF THE INVENTION
[0012] The present invention is directed generally to an apparatus
and method for the delivery of electrical current to a surgically
implanted device in a location in which bone growth is desired.
More specifically, the present invention discloses an electrical
bone growth promotion (EBGP) spinal fusion implant positioned
within the intervertebral space between two adjacent vertebrae of
the spine to promote and induce bone growth in the spinal fusion
process. The EBGP implant of the present invention comprises a
power supply and related control circuitry for delivering
electrical current directly to the housing of the EBGP implant
which is surgically implanted within the intervertebral space
between two adjacent vertebrae. The housing of the EBGP implant of
the present invention is at least in part electrically conductive
such that at least a portion thereof serves as an active cathode to
deliver negative charge directly to the spinal fusion site and to
any bone material contained within the EBGP implant and thus
directly to the area in which the promotion of bone growth is most
desired. As positive charges do not promote bone growth, but
actually induce resorption of bone, the areas of bone growth
promotion may be controlled either by conducting only negative
charges to the location for bone growth promotion is desired or by
conducting negative charges to the area in which bone growth
promotion is desired and at the same time conducting positive
charges to any area in which bone growth is to be inhibited. Thus,
the housing or a portion thereof, serves as an active cathode for
delivering negative charge or a combination active cathode and
active anode for delivering negative charge and for delivering
positive charge, respectively, to bone mass.
[0013] As an electrical bone growth promotion apparatus, the EBGP
implant of the present invention is not limited in its use with any
particular spinal fusion implant. Many different embodiments of the
EBGP implant of the present invention are possible. For example, in
a first embodiment of the EBGP implant, an implantable power supply
and related control circuitry are completely contained within a
hollow central chamber of the housing of the EBGP implant such that
the EBGP implant is a self-contained unit positioned within the
intervertebral space between two adjacent vertebrae of the spine
and may deliver electrical charge directly to the fusion site to
promote spinal arthrodesis. The power supply and control circuitry
may be contained in an extending portion of a cap used to close one
end of the hollow central chamber of the housing and thus may be
inserted into the EBGP implant which itself may in the remainder be
filled with bone.
[0014] The EBGP implant of the present invention is a
self-contained unit which overcomes the problems described above
associated with the prior art devices for delivering electrical
current to promote bone fusion. The EBGP implant of the present
invention conducts electrical current via its housing, or a portion
thereof, to an area of bone adjacent to the EBGP implant in which
the promotion of bone growth is desired. As no lead wires are
present, the problem of breakage of such wires experienced by the
devices of the past has been overcome. Further, as the power supply
and related control circuitry are fully contained within the EBGP
implant of the present invention there is no need to implant a
power supply and/or said related control circuitry at a remote
location from the EBGP implant. Further still, as the power supply
and related control circuitry become entombed in the bone mass upon
completion of the bone fusion process, no additional surgery is
required to explant the power supply and/or control circuitry as
was the case with the prior art. Thus, as no explantation is
required, the possibility of infection to the patient and other
risks inherent to all surgical procedures are eliminated, while
also substantially reducing the costs of utilizing electric current
to promote bone growth in the bone fusion process.
[0015] In a first variation of the first embodiment, the external
housing of the EBGP implant, the threaded portion, or any part of
the housing of the EBGP implant, may be utilized as an active
cathode by coupling the cathode lead from the power supply and/or
control circuitry contained within the EBGP implant to the housing
or a portion thereof. For example, the housing may be a spinal
fusion implant such as that described by Michelson in U.S. Pat. No.
5,015,247, issued on May 14, 1991, and could utilize its continuous
external thread much like a wound coil with the threaded portions
being separated from one another and from the remainder of the
spinal implant by an electrically non-conductive ceramic material,
and further that non-conductive material itself may also be
osteoinductive.
[0016] In a second variation of the first embodiment, the housing
of the EBGP implant further includes an opening through which bone
growth from one vertebra to a second adjacent vertebra may occur,
Coaxial with the opening is a coil that is coupled to the cathode
lead of the power supply. The coil acts as an active cathode to
deliver a negative charge and promote bone growth through the
opening and coil. In a further modification of this variation the
cathode continues as a coil about the housing of the EBGP.
[0017] In a second embodiment of the EBGP implant of the present
invention, any of a number of already known or conventional
surgically implantable power supply units and related control
circuitry may be placed within the body of the patient at a
location remote to the spine. A lead wire couples the power supply
and/or control circuitry to the housing of the EBGP implant, such
as a spinal fusion implant, situated within the intervertebral
space between and in contact with two adjacent vertebrae. The EBGP
implant which is at least in part not made of bone, and that part
also being electrically conductive, is used to conduct electrical
current to the interbody spinal fusion mass. In one variation of
the second embodiment, the entire housing of the EBGP implant is
electrically conductive and functions as an active cathode to
deliver negative charge to the area of bone adjacent thereto. In a
second variation of the second embodiment, the housing of the EBGP
implant may be made of a combination of electrically conductive and
non-conductive materials such that a first portion of the housing
of the EBGP implant is an active cathode specifically utilized for
the delivery of the negative electrical charge as discussed above
for the first variation of the first embodiment and a second
portion of the housing is an active anode specifically utilized to
deliver positive charge to the area in which bone growth is not
desired. The area of the anode may be minimized to reduce the area
in which bone growth is inhibited or may be larger such that the
anode is used to prevent bone formation over a substantial
area.
[0018] In order to make efficient use of the power supply, rather
than conducting electrical current to the entire housing of the
EBGP implant of the present invention which would require a large
power supply, electrical current may be conducted only to the
threads of the housing or to a wire coil insulated from the
remainder of the housing. In this manner less current is drained
from the power supply without reducing the effectiveness of the
electrical charge delivered to the site in which bone fusion is
desired since the electrical field created about the coil or
threads extends beyond the coil of the threads.
[0019] In a third embodiment of the EBGP implant of the present
invention, a spinal fusion implant is preferably implanted
surgically within the intervertebral space between two adjacent
vertebrae and is wholly or partially ferromagnetic. The spinal
fusion implant is hermetically sealed in a jacket composed of a
non-ferromagnetic, biocompatible material which may or may not be
electrically conductive. An electromagnetic field is produced by an
electromagnetic coil or coils worn external to the patient's body.
The spinal fusion implant may be inductively coupled to the
electromagnetic fields generated and transmitted by the external
coils, and thereby generate its own electromagnetic field and
accompanying electrical currents. These internal fields and
currents are localized within that segment of the spine in which
the spinal fusion implant is located, and will induce bone growth
and promote the spinal fusion process.
[0020] In a first variation of the third embodiment, the EBGP
implant is wholly or partially powered by electrical currents
induced within the EBGP implant by the externally-applied
electromagnetic fields. Likewise, any battery source integrated
into the EBGP implant may be recharged via such electromagnetic
induction to renew the service life of the battery source and thus
extend the period of time in which bone growth may be electrically
promoted. The EBGP implant in this embodiment delivers electrical
current and replenishes the power supply when inductively coupled
to externally applied electromagnetic fields.
[0021] In another embodiment of the EBGP implant of the present
invention, the power supply is surgically implanted within the body
of the patient, but at a location remote to the spine such as a
subcutaneous implantation, and is rechargeable in response to the
application of external magnetic fields.
[0022] In still another embodiment of the EBGP implant of the
present invention, the battery source is charged by an external
power source by ferromagnetic induction and continues to deliver
charges via that battery source even after the activity of the
external coil ceases.
OBJECTS OF THE PRESENT INVENTION
[0023] It is an object of the present invention to provide an
electrical bone growth promotion implant in which a power supply,
related control circuitry, and delivery system are entirely
self-contained within a spinal fusion implant, thus eliminating the
need to violate other body tissues to situate the implant, thereby
limiting the extent of surgery, the time for surgery, the blood
loss, and the risk of infection;
[0024] It is another object of the present invention to provide an
electrical bone growth promotion implant for delivering electrical
current to promote bone growth in a biomechanically and
biophysiologically optimal place so as to induce spinal fusion
within the compressive weight bearing axis of the spine;
[0025] It is yet another object of the present invention to provide
an electrical bone growth promotion implant that eliminates the
need for lead wires, the breakage of which has historically been a
major source of failure in regard to the use of electrostimulators
in general;
[0026] It is a further object of the present invention to provide
an electrical bone growth promotion implant in which with
successful arthrodesis, the encapsulated power supply and/or
related control circuitry becomes permanently entombed in the bone
fusion mass thus eliminating the need to perform a second surgical
procedure for its removal;
[0027] It is still a further object of the present invention to
provide an electrical bone growth promotion implant in which an
active cathode is fully contained within the bone fusion mass;
[0028] It is another object of the present invention to provide an
electrical bone growth promotion implant in which the power supply
and/or related control circuitry combined is an internal extension
of either a spinal fusion implant itself or of an insertable cap of
the spinal fusion implant;
[0029] It is a further object of the present invention to provide
an electrical bone growth promotion implant which will receive
externally applied electromagnetic fields and thereby generate
electromagnetic fields and electric currents affecting the bone
within and adjacent to the space between two adjacent vertebrae;
and
[0030] It is yet a further object of the present invention to
provide an electrical bone growth promotion implant in which the
power source for delivering electric current to the implant is
wholly or partially supplied or recharged by externally applied
electromagnetic fields.
[0031] These and other objects of the present invention will become
apparent from a review of the accompanying drawings and the
detailed description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is an exploded elevational side view, partially in
cross section, of the electrical bone growth promotion implant of
the present invention.
[0033] FIG. 2 is an elevational side view, partially in cross
section, of the electrical bone growth promotion implant of the
present invention inserted between two adjacent vertebrae of the
spine.
[0034] FIG. 3 is an alternative embodiment of the cap used for
closing the open end of the electrical bone growth promotion
implant of the present invention.
[0035] FIG. 3A is an enlarged fragmentary view along line 3A of
FIG. 1 showing in cross section the end of the casing.
[0036] FIG. 4 is a side elevational view, partially in cross
section, of a first alternative embodiment of the electrical bone
growth promotion implant of the present invention having one end in
which a portion thereof is made of a non-conductive material and
insulated from the rest of the implant such that different
polarities of electrical charges may be delivered to different
parts of the implant as illustrated by the electrical field
arrows.
[0037] FIG. 5 is an end view of the electrical bone growth
promotion implant of the present invention along line 5-5 of FIG.
4.
[0038] FIG. 6 is a cross sectional, side elevational view of a
second alternative embodiment of the electrical bone growth
promotion implant of the present invention having a cap at one end
in which a portion thereof is made of non-electrically conductive
material.
[0039] FIG. 7 is a side elevational view of a third alternative
embodiment of the electrical bone growth promotion implant of the
present invention having outer threaded portions that are separated
from the rest of the implant by a non-electrically conductive
insulating material.
[0040] FIG. 8A is an enlarged fragmentary cross sectional view of
the third alternative embodiment of the electrical bone growth
promotion implant taken along line 8 of FIG. 7 showing the threaded
portion being anchored to the non-electrically conductive
material.
[0041] FIG. 8B is an enlarged fragmentary cross sectional view of
the third alternative embodiment of the electrical bone growth
promotion implant taken along line 8 of FIG. 7 showing the thread
portion being anchored to and passing through a non-conductive
material.
[0042] FIG. 9 is a side elevational view of a fourth alternative
embodiment of the electrical bone growth promotion implant of the
present invention having an external wire coil interposed between
the external threads of the implant and insulated from the
remainder of the implant by an non-electrically conductive
insulating material.
[0043] FIG. 10 is an enlarged fragmentary view taken along line 10
of FIG. 9 showing the external wire coil being held in place
between the external threads of the implant by a non-electrically
conductive insulating material.
[0044] FIG. 11 is a perspective view of a fifth alternative
embodiment of the electrical bone growth promotion implant of the
present invention having an opening surrounded by a wire coil
coaxial with the opening electrically connected to a remote power
source.
[0045] FIG. 12 is a side view of a sixth alternative embodiment of
the electrical bone growth promotion implant of the present
invention having an opening surrounded by a wire coil coaxial with
the opening and electrically coupled to an internal power
source.
[0046] FIG. 13 is a top plan view of the electrical bone growth
promotion implant of FIG. 12 showing the opening.
[0047] FIG. 14 is a cross sectional side elevation view along lines
14-14 of FIG. 11 of the bone growth promotion implant of the
present invention having an external power source and illustrating
the bone growth from one vertebra to a second adjacent vertebra
that occurs during the spinal fusion process.
[0048] FIG. 15 is a perspective view of a structural support member
used to support a wire coil coaxial with the vertical opening of
the electric bone growth promotion implant of the present
invention.
[0049] FIG. 16 is a cross sectional side elevational view of a
seventh alternative embodiment of the electrical bone growth
promotion implant of the present invention having an insulated cap
at one end, a cathode lead from an external power supply connected
to.
[0050] FIG. 17 is an end view of the seventh alternative embodiment
of the electrical bone growth promotion implant along 17-17 of FIG.
16.
[0051] FIG. 18 is a front elevational view of an externally worn
electromagnetic energy transmitter for transmitting an
electromagnetic field to an implanted spinal fusion implant.
[0052] FIG. 19 is a cross sectional view taken along lines 19-19 of
FIG. 18 illustrating the transmission of electromagnetic energy
generated by the electromagnetic energy transmitter to a spinal
fusion implant positioned within the patient's spine.
[0053] FIG. 20 is a perspective side view of an eighth alternative
embodiment of the electric bone growth promotion implant of the
present invention having an internal power supply and generator
shown in hidden line.
[0054] FIG. 21 is a perspective view of a ninth alternative
embodiment of the electric bone growth promotion implant of the
present invention having an internal power supply and generator
shown in hidden line.
DETAILED DESCRIPTION OF THE DRAWINGS
[0055] Referring to FIGS. 1 and 2, the electrical bone growth
promotion (EBGP) implant of the present invention is shown and is
generally referred to by the numeral 10. In the preferred
embodiment, the EBGP implant 10 comprises a housing 30 as shown in
FIG. 2 which is implanted in the intervertebral disc space S
between adjacent vertebrae V.sub.1 and V.sub.2 in a segment of the
spine for achieving arthrodesis.
[0056] As shown in FIG. 1, housing 30 includes a hollow tubular
body that is at least partially cylindrical having side walls 34
and preferably made of an surgically implantable and electrically
conductive material such as, but not limited to, titanium. The
housing 30 has a hollow central chamber 36 that is open at its
distal end 38, is closed at its proximal end 40 and has a series of
macro-sized openings 42 perforating the side walls 34. The
macro-sized openings 42 preferably have a diameter in the range of
approximately 2.0 mm to approximately 6.0 mm to allow for the macro
fixation of the adjacent vertebrae V.sub.1 and V.sub.2. During the
fusion process, bone growth occurs from each of the two adjacent
vertebrae V.sub.1 and V.sub.2 through the macro-sized openings 42
to any natural or artificial bone fusion enhancing material that
may be contained within the central chamber 36 so as to form a
single solid mass.
[0057] The housing 30 has a similar structure and configuration of
a spinal implant such as, but not limited to, the spinal fusion
implant taught by Michelson in U.S. Pat. No. 5,015,247. The housing
30 is preferably, at least in part, electrically conductive and is
made of material stronger than bone to provide structural support
to the two adjacent vertebrae V.sub.1 and V.sub.2 while awaiting
bone ingrowth, becoming firmly and permanently fixed in place once
bone growth has occurred. To further enhance bone growth, the
housing 30 may be coated with a bone growth inducing material such
as, but not limited to, hydroxyapatite, hydroxyapatite tricalcium
phosphate, bone morphogenic protein and the like. The housing 30
may also have a surface configuration that enhances bone growth
such as, but not limited to surface knurling or roughening.
[0058] The open distal end 38 has internal threads 39 and is
closeable with a cap 50 having at least a portion thereof that is
electrically conductive. The cap 50 has a threaded end 52 which is
threaded to match the internal threads 39 and secured to internal
threads 39 by the use of a driver/wrench W or an equivalent
tool.
[0059] Attached to and extending from the cap 50 is a casing 80 for
containing electrical components discussed in greater detail below.
The casing 80 is appropriately sized such that it fits within the
central hollow chamber 36 of the housing 30 and occupies the least
amount of space possible so as to limit interference with the bone
fusion process. When the cap 50 is threadably coupled to the
housing 30, the casing 80 is completely contained within the
central hollow chamber 36 such that the EBGP implant 10 is a
self-contained unit.
[0060] Referring to FIG. 2, the EBGP implant 10 is shown surgically
implanted in the disc space S between the two adjacent vertebrae
V.sub.1 and V.sub.2. At least a portion of the housing 30 is
embedded into the bone of the adjacent vertebrae V.sub.1 and
V.sub.2. However, it is appreciated that for the purpose of the
present invention, the housing 30 need not be embedded into the
bone of the vertebrae V.sub.1 and V.sub.2, but need only be placed
adjacent to and be in contact with the vertebrae V.sub.1 and
V.sub.2 in order to enable the EBGP implant 10 to conduct
electrical current to the adjacent vertebrae V.sub.1 and
V.sub.2.
[0061] It is to be understood that electrical current is a function
of the time rate of change of electrical charge and the terms
current and charge may be alternatively used depending upon context
in describing the EBGP implants of the present invention. Further,
as charge is proportional to the resistance encountered by the
current, as bone growth occurs the resistance encountered by the
current delivered to the bone mass will be increased, such that the
charge will decrease. Also as the power supply depletes, the amount
of current delivered over time will also decrease.
[0062] The hollow central chamber 36 can be filled with and may
hold any natural or artificial osteoconductive, osteoinductive,
osteogenic, or other fusion enhancing material. For example, bone
material B harvested from the patient may be loaded into the
central hollow chamber 36 as well as packed around the exterior of
the housing 30, but within the intervertebral disc space S, wherein
it is utilized in the spinal fusion process. An obdurator or
similar instrument may be used to create a space in the bone
material B for receiving an object therein such as the casing 80.
In this manner, the housing 30 may be filled with bone material B
and then closed with the cap 50 to hold the bone material B within
the hollow chamber 36 during surgical implantation.
[0063] The casing 80 itself, or a portion thereof, is made of an
electrically conductive and surgically implantable material such
as, but not limited to, titanium such that electrical current
applied to the casing 80 may be transferred from the casing 80 to
the bone material B that is contained within the hollow central
chamber 36. The casing 80 may be removably attached to the cap 50
or may be permanently affixed. In the preferred embodiment, the
casing 80 is electrically coupled to the cap 50. However, it is
appreciated that the casing 80 may be electrically insulated from
the cap 50 if it is not desired to conduct an electrical current to
the cap 50 or if it is desired to conduct an electrical current to
the cap 50 having a different polarity from the remainder of the
casing 80.
[0064] Within the casing 80 are the electrical components
comprising a power supply 60, control circuitry 70, a cathode lead
72, and an anode lead 74. Both the power supply 60 and the control
circuitry 70 are fully implantable and hermetically sealed. The
cathode lead 72 is electrically coupled to the cap 50 either
directly or via the casing 80, such that when the cap 50 is
threaded to the housing 30, negative electrical charge is
transferred to the housing 30 such that the housing 30 itself
becomes an active cathode. In this manner, the power supply 60 is
electrically coupled to the housing 30 and is located at the site
in which spinal fusion is desired. Thus, in this embodiment, the
EBGP implant 10 is a self-contained unit, thereby eliminating the
need to implant the power supply 60 and related control circuitry
70 at a remote location within the patient's body, as is the case
with fusion stimulators of the prior art.
[0065] The control circuitry 70 preferably includes well known
means for the delivery of a constant current source, providing a
single, preset current in the range of 0.01 to 20 uA. Thus, neither
attachment of multiple cathodes or variation in cathodic area will
alter the current density delivered to the bone fusion mass. It is
appreciated that the control circuitry 70 may also include a wave
form generator, a voltage generator or a clock means for delivering
intermittent pulses of current with out departing from the scope of
the present invention. Alternatively, the control circuitry 70 may
comprise means for providing various patterns of direct current,
alternating current, pulsatile current, sinusoidal current, or
electrical noise generated by current rather than constant, direct
current in order to promote bone growth. It is further appreciated
that the electrical components may also comprise any of the
well-known devices currently available to electrically stimulate
spinal fusion, such as but not limited to the stimulator available
from EBI Medical Systems, Parsippany, N.J., and may also be any of
the devices suitable for delivering electric current and suitable
for implantation well-known by those skilled in the art.
[0066] The control circuitry 70 is powered by the fully
implantable, hermetically sealed power supply 60 which may be any
of the well-known power supplies known in the art and currently
commercially available and used to electrically promote spinal
fusion such as, but not limited to, the power supply by EBI Medical
Systems, Parsippany, N.J. The power supply 60 also may contain
circuitry for generating electrical charge in response to
externally applied electromagnetic fields.
[0067] Referring to FIG. 3, alternatively, the power supply 60' may
include battery recharge circuitry responsive to externally applied
electromagnetic fields for recharging the battery. As a
consequence, the overall size of the power supply 60' may be
substantially reduced with a corresponding reduction in the size of
the casing 80'. In this manner, any interference with the bone
fusion process by the casing 80' is further reduced. Moreover, the
longevity of the power supply 60' may be substantially increased as
the power supply 60' may be recharged to extend its life beyond
that of a conventional non-rechargeable battery having a fixed
service life. As a result, the electric promotion of osteogenesis
may be extended beyond the service life of conventional prior art
devices with their non-rechargeable batteries. Further, the
rechargeable power supply 60' may be reduced in size as the service
life may be extended indefinitely, compactness of power supply such
that bone growth promoting bone material is not displaced which is
essential for fusion.
[0068] Also shown in FIG. 3, is an alternative embodiment of the
cap 50' which may be secured to the housing 30 by a spring
fastening means 52' which engages the interior surface of the
housing 30 once the spring fastening means 52' is inserted in the
central hollow chamber 36. In this embodiment, the time required to
load bone material B within the central hollow chamber 36 and the
time to assemble the cap 50' to the housing 30 is significantly
reduced.
[0069] As shown in FIG. 3A, the end of the casing 80 includes an
insulated screw 90 made of a non-conductive material. The screw 90
has a threaded portion 92 which threadably attaches to the casing
80, and has an electrically conductive core 94 passing through the
longitudinal axis of the screw 90. The electrically conductive core
94 terminates at one end into an electrically conductive head
portion 96 and is at its other end electrically coupled to the
anode lead 74. In this manner, the head portion 96 becomes the
active anode for delivering positive electrical charge to an area
of bone. As previously noted positive electrical charge inhibits
osteogenesis, the head portion 96 preferably has the smallest
possible size to limit the area of contact to bone exposed to
positive charge to limit bone resorption and is positioned at a
location where the presence of positive charge will least interfere
with the fusion process.
[0070] In the preferred embodiment, the head portion 96 is located
at the tip of the end of the casing 80 such that when the cap 50 is
attached to the housing 30, the head portion 96, and thus the
active anode, is at a location which least interferes with the
electrical promotion of the bone material B contained with the
central chamber 36 and has substantially no contact with the
adjacent vertebrae V.sub.1 and V.sub.2 to which fusion is desired.
An example of the electrical current present in the EBGP implant 10
is illustrated by the electrical field arrows in FIG. 2.
[0071] As the promotion of bone growth occurs by the application of
negative electrical current, the promotion of bone growth may be
controlled by the application of negative electrical current only
to the location in which bone growth is desired. For example, if
bone growth promotion is desired at a particular location, negative
current may be transferred to the housing 30 or a portion thereof
which is adjacent to and in contact with a desired site in order to
accelerate the fusion process. In areas where bone growth is not
desired, such as near the canal of the spine for example, positive
current may be transferred to the desired site.
[0072] Referring again to FIG. 1, in order to conduct positive
charge from the head portion 96 (the active anode) the presence of
which is undesired within the central hollow chamber 36, an
insulated screw 20 having a conductive inner core 22 is threaded
through an opening 24 in the proximal end 40. The insulated screw
20 has a recess 26 for receiving and coupling to the head portion
96. In this manner, positive charge is conducted by the conductive
inner core 22 to a point external to the housing 30.
[0073] Referring to FIGS. 4 and 5, a first alternative embodiment
of the EBGP implant is shown and generally referred to by the
numeral 110. The EBGP implant 110 comprises a housing 130 similar
to the housing 30 described above, except that it has a proximal
end 140 that is at least in part insulated from the remainder of
the housing 130. The housing 130 has macro-sized openings 142 to
permit bone growth therethrough. Anode lead 174 from the power
supply 160 and/or control circuitry 170 may be electrically coupled
to the proximal end 140 of the housing 130 so that the proximal end
140 may be positively charged. To accomplish this, the proximal end
140 has a screw 120 having a conductive screw head 121, a
conductive inner core 122, and an insulated stem portion 123 having
a recess 126 for coupling to the head portion 196 (the active
anode.) The inner core 122 conducts positive charge from the head
portion 196 to the conductive screw head 121. The screw head 121 is
insulated from the housing 130 by an insulated ring 125 made of a
non-electrically conductive material so that the screw head 121 can
conduct positive charge to a point external to the housing 130 so
that at least a portion of the proximal end 140 of the housing 130
becomes positively charged as illustrated by the electrical field
arrows in FIG. 4. In this manner, the area of positive charge may
be varied in size by varying the area of the screw head 121, and
thus the area of potential promotion of bone resorption is also
variable. As shown in FIG. 4, the area of screw head 121 has been
deliberately increased to inhibit bone formation in an area
adjacent to the screw head 121.
[0074] The configuration of electrical charges shown in the EBGP
implant 110 would be utilized when the housing 130 is installed
from the posterior aspect of the spine toward the anterior aspect
of the spine since the proximal end 140 of the EBGP implant 110
would be proximate to the spinal canal once implanted in the disc
space S between two adjacent vertebrae V.sub.1 and V.sub.2. By
conducting positive charges to the proximal end 140 osteogenesis in
the spinal canal which could compress the neural structures is
inhibited.
[0075] It is appreciated that where negative electrical charge for
the purpose of promoting bone growth is desired generally along the
entire EBGP implant 110, then the positively charged screw 120
would have a screw head 121 proportionally much smaller in size to
limit the area of positive electrical charge.
[0076] For the areas adjacent to the housing 130 in which bone
growth and fusion is desired, the cathode lead 172 from the power
supply 160 and/or control circuitry 170 is coupled to the casing
180 and negative charges are conducted to the housing 130 by the
contact of the casing 180 and cap 150 with the housing 130 such
that the housing 130 itself becomes an active cathode.
[0077] It is further appreciated that the delivering of positive
charges and the negative charges may be reversed simply by
interchanging the anode lead 174 and the cathode lead 172 coupling
points to the housing 130, cap 150, distal end 140, or screw 120.
In this way, negative charge may be applied and directed only to
the particular areas in which bone growth is desired depending on
the type of surgery, bone growth, and fusion desired.
[0078] Referring to FIG. 6, for example, if the EBGP implant 110 is
installed from the anterior aspect toward the posterior aspect of
the spine, the distal end 138 of the housing 130 would be proximate
to the spinal canal. In order to prevent undesired bone growth near
the spinal canal, the distal end 138 of the housing 130 or a
portion thereof, which when implanted is adjacent to and in contact
with the bone near the housing 130, may be insulated from the
remainder of the housing 130. Further, the distal end 138 may be
positively charged by being connected to the anode lead 174 of the
generator 160 so that the proximal end 138 itself serves as an
active anode. This can be accomplished by having an insulated screw
156 having an electrically conductive core 158. The electrically
conductive core 158 becomes the active anode and delivers positive
electrical charge to the adjacent bone area. Thus, bone area
adjacent to and in contact with the distal end 138 would be exposed
only to positive charge and not to bone growth promoting negative
charge. Further, in order to minimize bone resorption, the diameter
of the electrically conductive core 158 may extend from the
insulated screw 156 and may be decreased in size to limit the bone
area being exposed to positive electrical charge.
[0079] The application of different polarity charges to different
areas of the housing 130 may also be accomplished by having the
threads 152 of a cap 150 coated with a non-conductive material such
as, but not limited to, a ceramic material in order to insulate the
cap 150 from the remainder of the housing 130 such that the cap 150
becomes the active anode when connected to the anode lead 174 and
is positively charged. This will prevent electrical promotion of
bone growth in the vicinity of the cap 150 which is adjacent to the
spinal canal and in contact with the bone near the spinal canal
when implanted. However, it is appreciated that other means of
insulating the distal end 138 well-known by those skilled in the
art, may be employed so that the distal end 138 has a different
charge than the remainder of the housing 130 or has no charge at
all.
[0080] Referring to FIGS. 7, 8A and 8B, a second alternative
embodiment of the EBGP implant of the present invention is shown
and generally referred to by the numeral 210. The EBGP implant 210
comprises a housing 230 similar to the housing 30 described above.
The exterior of the housing 230 has external threads 200 which are
formed on the outer circumference of the housing 230 preferably in
a helix.
[0081] As shown in FIG. 8A, the threads 200 of the housing 230 are
electrically conductive and have a non-conductive insulating
material 202 separating the threads 200. The insulating material
202 may be ceramic or polyethylene or any other biocompatible
material that has electrical insulating properties. In this second
alternative embodiment, the housing 230 may be completely or
partially hollow and threads 200 serve as the active cathode to
conduct negative charge to the bone area in which the housing 230
is implanted and any material that may be within the housing 230.
As the insulating material 202 is interposed between the threads
200 themselves and between the housing 230 itself, the threads 200
are isolated from the remainder of the housing 230 and essentially
act as a coil that surrounds the exterior of the housing 230. The
threads 200 are electrically connected to the cathode lead 74 (see
FIG. 1) of the control circuitry 70 described above and thus the
threads 200 function as a cathode to deliver negative charge from
the EBGP implant 210 to the vertebrae V adjacent to the housing 230
and material contained within the housing 230 if any. The advantage
of this arrangement is that only the coil threads 200 are charged
rather than the external housing 230 and since the beneficial
electrical effect to some instance from each of the threads 200,
the threads 200 are an effective cathode lead with less current
drain than would be required to charge the external housing
230.
[0082] As shown in FIG. 8B, it is possible to configure the threads
200 such that at least a portion thereof passes through the
insulating material 202 and communicates with the central chamber
236 so as to also conduct electric charge to any material contained
within the housing 230 as illustrated by the electrical field
arrows. This design requires that either the inward or outward
portions of the threads 200 not be continuous such that the
integrity of the housing 230 is not substantially reduced. The
housing 230 has macro-size openings 242 to permit bone-growth
therethrough.
[0083] Referring to FIGS. 9 and 10, a third alternative embodiment
of the EBGP implant 310 of the present invention is shown and is
generally referred to by the numeral 310. In the third embodiment,
the EBGP implant 310 comprises a housing 330 similar to the housing
30 described above, having threads 300 and a wire 350 placed
between the threads 300. The wire 350 is supported by a non
conductive insulating material 364 that is placed between the
threads 300 of the housing 330. The insulating material 364 has a
groove 362 for receiving and holding the wire 350. The wire 350 is
electrically coupled to a cathode lead such as the cathode lead 72
of the generator 60 (shown in FIG. 1) and is negatively charged
such that wire 350 conducts bone growth promoting negative charge
to the bone area of the adjacent vertebrae V.sub.1 and V.sub.2
adjacent to the coiled wire 350 and through the openings 342 to the
fusion mass within the housing 330. The insulating material 364
prevents the body of the housing 330 from becoming electrically
charged and prevents electrical conduction between wire 350 and
threads 300 and housing 330 and any short circuiting of the coiled
wire 350. In this manner, the area of the EBGP implant 310 which is
electively charged is limited to the coiled wire 350 to
significantly reduce the total area which is electrically charged.
However, as the coiled wire 350 essentially extends approximately
the entire longitudinal length of the EBGP 310, it is possible to
deliver electrical charge to the entire area of bone adjacent to
the EBGP 310 to stimulate bone growth without any diminished
effect. Thus, the EBGP implant 310 is energy efficient since the
amount of electrical current required to power the EBGP implant 310
is substantially less than that required for an implant where the
entire implant housing is charged.
[0084] Referring to FIGS. 11-15, a fourth alternative embodiment of
the EBGP implant 410 of the present invention is shown and is
generally referred to by the numeral 410. In the fourth embodiment,
the EBGP implant 410 comprises a housing 430 similar to the housing
30 and having an opening 420 having an axis that is perpendicular
to the longitudinal axis L of the housing 430. The opening 420
passes through the housing 430 and communicates with the central
chamber 436 of the housing 430 and is surrounded by four structural
support members 421, 422, 423, and 424. The opening 420 is covered
by a lattice 415 at both ends. The lattice 415 has openings 416
sufficiently sized to permit bone growth therethrough yet remains
capable of retaining any natural or artificial bone growth material
that may be contained within the hollow central chamber 436.
[0085] Referring to FIG. 15, an enlarged perspective view of
structural support member 421 is shown. Each of the structural
support members 421, 422, 423, and 424 are identical such that the
description of one applies to each of the others. The structural
support member 421 made of an electrically non-conductive material,
has an upper arm 440 and a lower arm 442 that are placed in the
hollow central chamber 436 and are secured to the spinal implant
410; a central portion 443 having a curved outer edge 444; and a
grooved inner edge 446. The inner edge 446 of the structural
support member 421 has a plurality of grooves 448 for receiving and
holding a wire 425 capable of conducting electrical current. The
plurality of grooves 448 are offset from each other and follow the
curvature of the outer edge 444 of the structural support member
421.
[0086] Referring back to FIG. 11, preferably the four structural
support members 421-424 are arranged around the outer perimeter of
the opening 420 such that they are equidistant from one another.
The wire 425 is placed within the grooves 448 and coiled about the
four structural support members 421-424 to form a wire coil 426
around the perimeter of the opening 420 substantially along the
entire vertical length of the opening 420 that is coaxial with the
opening 420.
[0087] The wire coil 426 is electrically coupled to a cathode lead
472 and delivers and delivers a negative charge to the area
surrounding within the torroid opening 420 such that bone growth is
promoted and stimulated by the presence of negative charge along
the inner and outer walls of the torroid shaped wire coil 426. When
the EBGP implant 410 is implanted between two adjacent vertebrae
V.sub.1 and V.sub.2, the opening 420 is filled with bone or bone
promotion substances and the electrical promotion of bone growth
causes bone of the adjacent vertebrae V.sub.1 and V.sub.2 to grow
into and through the vertical opening 420 into that bone or bone
promoting substances from one vertebra V.sub.1 to the other
vertebrae V.sub.2.
[0088] As shown in FIGS. 12 and 13, the control circuitry 470 and
the power supply 460 are contained within the central chamber 436
of the housing 430 such that the EBGP implant 410 is a
self-contained unit. The wire coil 426 is coupled directly to a
cathode lead 472 such that the wire coil 426 becomes negatively
charged.
[0089] As shown in FIGS. 11 and 14, alternatively, the control
circuitry 470 and power supply 460 may be implanted in an area of
the patient's body remote from the EBGP implant 410. The cathode
lead 472 may be coupled directly to the wire coil 426 via lead wire
462 or may be coupled to the body of the housing 430 which is
electrically conductive, and the wire coil 426 may also be
electrically coupled to the housing 430 so that the housing 430
becomes electrically charged. However, it is preferred that the
wire coil 426 be connected to either a wire coil such as described
above in reference to FIGS. 9 and 10 or threads 200 as described
above in reference to FIGS. 7, 8A and 8B. In this manner, efficient
use of the power supply 460 is made as the drain is reduced without
diminishing the effectiveness of the electrical promotion of bone
growth as discussed above.
[0090] Referring to FIGS. 16 and 17 a fifth alternative embodiment
of the EBGP implant 510 of the present invention is shown. The EBGP
implant 510 comprises a housing 530 having a non-electrically
conductive cap 550 threaded to its distal end 538, and a remotely
implanted power supply 560 and control circuitry 570 connected to
the housing 530. As the cap 550 is non-conductive, the housing 530
itself is negatively charged when coupled to the cathode lead 572
and the cap 550 has no electrical charge. The power supply 560 is
electrically connected to the housing 530 by the lead wire 562
which terminates at a connector 590 which is attached by a screw
592 to the housing 530.
[0091] It is appreciated that a remotely implanted power supply
and/or related control circuitry may be used to deliver electric
current to any of the embodiments described above that are
self-contained units having an internal power supply and generator,
without departing from the scope of the present invention.
[0092] Referring to FIGS. 18 and 19 a sixth alternative embodiment
of the EBGP system 612 of the present invention is shown. In the
sixth alternative embodiment, the EBGP implant 610 comprises an
electromagnetic field transmitter 600 that is worn external to the
patient's body. The transmitter 600 has two portions 602 and 604
which are secured to the patient's body by a band 606 or any other
suitable means, such that each portion 602, 604 is placed on
opposite sides of the body at the exterior of the patient's
body.
[0093] Implanted between two adjacent vertebrae V.sub.1 and V.sub.2
of the patient is a housing 630 similar to the housing 30 described
above. The housing 630 is at least in part ferromagnetic and
thereby capable of being inductively coupled to the electromagnetic
fields transmitted by the transmitter 600. The EBGP implant 610
thereby may be inductively coupled to transmitter 600 and in this
manner electromagnetic fields and resultant induced electrical
currents in EBGP implant 610 may be concentrated and directed to a
location in which bone growth is desired without the need for
surgically implanting a power supply and/or control circuitry
within the housing 630 or within the body of the patient. The
non-ferromagnetic portion of the housing 630 also may be
electrically conductive, which would make the housing 630 capable
of being inductively coupled to the electromagnetic fields
transmitted by the transmitter 600 as well as a conductor of
electrical currents induced by said externally applied
electromagnetic fields.
[0094] Similarly, if a rechargeable power supply 460 (FIG. 12) is
contained within the housing 630, the power supply may be recharged
with the application of external electromagnetic fields via the
transmitter 600. Thus, the power supply in implant 610 could be
much smaller in size as the power supply may be repeatedly
recharged. In this manner, both the housing 630 and the power
supply therein may be inductively coupled to the transmitter 600,
such that the housing 630 delivers electrical current to the
adjacent bone mass and the power supply is being recharged. After
the transmitter 600 is no longer inductively coupled to the EBGP
implant 610 the replenished power supply in implant 610 continues
to deliver electrical current to the housing 630. In this manner,
the period of time in which a patient must wear the transmitter is
substantially reduced to the period of time required to replenish
the power supply, while maintaining a continuous delivery of
electrical current to the housing 630.
[0095] As a further alternative, a rechargeable power supply may be
implanted remote to the spine, preferably subcutaneously, such that
the power supply is easily rechargeable via electromagnetic
induction. The inductive coupling of a subcutaneous power supply
with the electromagnetic transmitter 600 overcomes the problems of
infection associated with any direct coupling of a power supply to
a power source. Further, subcutaneous implantation of the power
supply also facilitates explantation of the power supply and
further reduces the risk of infection to the patient. In contrast
to implantations in other areas of the body.
[0096] Referring to FIG. 20 a seventh alternative embodiment of the
EBGP implant 710 of the present invention is shown. In the seventh
embodiment, the housing 730 has a substantially rectangular hollow
configuration and has a tapered distal end 738. The housing 730 has
an upper surface 750 and a parallel lower surface 752 and two side
walls 754 and 756. The housing 730 has a series of small openings
742 through the upper and lower surfaces 750 and 752 and through
the side walls 754 and 756 for permitting bone growth there
through. Contained within the spinal implant 710 are the power
supply 760 and the control circuitry 770 so that the spinal implant
730 is a self-contained unit. The power supply 760 and/or control
circuitry 770 are electrically coupled to the housing 730 by a
cathode lead 772 and an anode lead 774. The anode lead 774 is
coupled to an insulating screw 790 having an electrically
conductive core 796. The insulating screw 790 is threaded into the
EBGP implant 710 and insulates the anode lead 774 from the rest of
the EBGP implant 710.
[0097] Referring to FIG. 21 an eighth alternative embodiment of the
EBGP implant 810 of the present invention is shown. The EBGP
implant 810 is much like the seventh alternative embodiment except
that the housing 830 has a hollow rectangular configuration with
raised engagement teeth 880 for engaging the bone of adjacent
vertebra V and has a wire 850 similar to wire 350 described above,
coiled about the housing 830. The wire 850 is insulated from the
housing 830 by an insulating material 864 having a groove 862 for
receiving the wire 850. The insulating material 864 is identical to
insulating material 364 discussed above. The EBGP implant 810 is
also a self-contained unit as the power supply 860 and/or the
control circuitry 870 are contained within the hollow chamber of
the spinal implant 810 and are electrically coupled to the wire
850.
[0098] It is appreciated that the EBGP implant of the present
invention is not limited to use in the spinal fusion process but is
also applicable to promoting almost any fusion of a large joint and
for promoting healing of a fracture of any of the major bones of
the body. Furthermore, the apparatus and method of the present
invention may be incorporated into various total knee arthroplasty
and total hip arthroplasty. Such implants may embody the
above-described teachings without departing from the scope of the
present invention. Such implants may be wholly or partially
electrically conductive having a permanent or rechargeable power
supply and related control circuitry located within the implant
itself such that the implant is a self-contained unit. The use of a
renewable power source is of great advantage with such implants in
that the bone fusion process, or the healing of the larger bones
such as the femur or hip, for example, may require a longer period
of time for bone healing fusion than the service life of the
implantable permanent power supplies that are presently utilized.
As discussed above in greater detail, the recharging of the power
source through external charging can extend the delivery of
electrical current to the site in which induction of osteogenesis
is desired for a substantially greater period of time.
[0099] Further, such implants may also comprise externally applied
electromagnetic coils to generate an electromagnetic field that may
be inductively coupled to the implant which in turn delivers
electrical charges to the areas of bone adjacent to the implant as
described in greater detail above and recharge the power supply by
electromagnetic induction from an externally applied electrical
field. All of such implants have the added advantage in that once
implanted they become permanently entombed within the bone fusion
mass after completion of the fusion process and need not be
surgically removed.
[0100] While the present invention has been described in detail
with regards to the preferred embodiments, it is appreciated that
other variations of the present invention may be devised which do
not depart from the inventive concept of the present invention.
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